1. Field of the Invention
This invention relates to universal serial bus (USB) use, and more particularly to a method and apparatus of balancing available USB bandwidth for USB devices.
2. Description of the Related Art
In many of todays processing systems, such as personal computer (PC) systems, there exist USB ports for connecting various USB devices. Some of these USB devices are frequently used by PC users. For example, these USB devices may be printers, compact disk read-only-memory (CD-ROM) drives, CD-ROM Writer (CDRW) drives, digital versatile disk (DVD) drives, cameras, pointing devices (e.g., computer mouse), keyboards, joy-sticks, hard-drives, speakers, etc. Some of these devices use more of the available USB bandwidth than others. For example, a USB CDRW is a high bandwidth device, while human interface devices (HID), such as computer mice, keyboards and joysticks, are low bandwidth devices.
Different standards of USB technology have different bandwidths. For example, Universal Serial Bus Specification, revision 1.1, Sep. 23, 1998 (USB 1.1) devices are capable of operating at 12 Mbits/second (Mbps), and Universal Serial Bus Specification, revision 2.0, Apr. 27, 2000 (USB 2.0; also known as high-speed USB) devices are capable of operating at 480 Mbps. Many users of PCs may not understand how to plug in USB devices into the PCs such that two high-bandwidth devices are not sharing the same root hub. When different devices share the same root hub, the devices also must share/split the bandwidth of the USB.
For example, if a user wishes to use a USB CDRW and a USB hard drive, (both are high bandwidth devices) and the user plugs both devices into the USB PC ports that share the same root hub, the hard drive and CDRW, will operate at approximately half of their associated maximum speed capability when simultaneously used. Therefore, assuming both devices are USB 1.1 devices, the throughput is divided in half due to a shared root hub. Thus, the devices may only operate at a rate of 6 Mbps when used simultaneously, instead of the maximum rate of 12 Mbps.